1 Steve Jobs was a perfectionist
Steve Jobs, Apple's founder, was a perfectionist who always used to set extremely high quality standards for people. Jobs hardly liked anything and always wanted to see perfect products.
2 Apple targets certain customers
Apple targets certain customers with its products. An Apple product is usually much more expensive than that of a competing company. Because of that strategy, the product has have to superior quality so that people believe the product deserves their money (See why the Apple watch is so expensive).
3 Steve Jobs used to fire people with mediocre outputs
Steve Jobs used to fire people who didn't produce high quality work. The result was that people understood that Apple is a place where high quality work is expected (See why Steve Jobs used to fire people).
4 Quality is part of the company's culture
During his years at Apple, Jobs managed to set extremely high standards of quality that it became an integral part of the company's culture.
5 The company pays extreme attention to detail
All Apple products are designed with extreme attention to detail. During the manufacturing of the Apple computer, Steve Jobs pushed people to make the inside of the computer as beautiful as the outside even though they knew people won't open it (See how the Apple I computer was created).
6 Jobs wanted to change the world
Steve Jobs made it clear that he wanted to change the world with his products, and because of that desire he focused on creating very high quality products so that they can easily become popular (See also how Steve Jobs started Apple).
7 Apple has a closed ecosystem
In a closed ecosystem it's much easier to control the quality standards of a product. Steve jobs insisted that Apple adopts a closed system and this approach helped the company keep its quality standards very high (see Why isn't apple open source).